1. Field of the Invention
This invention relates to steam turbine power plants, and, in particular, to a steam turbine power plant having associated therewith an associated closed loop flow arrangement for extracting heat from the power plant and supplying the heat so extracted to an external heat load.
2. Description of the Prior Art
Recently, emphasis has been placed on the realization of an economically attractive "dual-purpose" power generation facility adapted to fulfill a two-pronged goal of simultaneous electric power generation and brine desalinization. In such dual purpose facilities, it has been anticipated that the motive fluid for the electric power generation be supplied by a nuclear powered steam generator, while the desalinization of brine is effectuated by the application of the "flash evaporation" process.
Briefly, flash evaporation is a multi-stage distillation process in which sea water is progressively heated to a predetermined temperature under given pressure conditions and then introduced into a chamber maintained at a lower pressure just below the boiling point of the heated brine. As the heated brine enters the lower pressure chamber, the reduced pressure therein causes the brine solution to boil, or "flash", into steam. The steam so produced is condensed and the fresh water produced thereby is conducted away. It has been anticipated that the heat necessary to raise the temperature level of the brine be extracted from the nuclear-fuel steam turbine power plant.
In the prior art, it is common practice to raise the temperature of the brine solution by conducting steam from one predetermined extraction location within the power plant directly to the brine heat exchanger. The heat of the extracted steam is there transferred to the brine. The condensate is returned to the steam cycle.
Although direct steam extraction techniques have been successful on small scale (50 megawatt or less) power stations, they have little applicability for large capacity water desalinization power plants. Also, extraction of volumes of steam larger than a predetermined amount from only one location within the power plant may deleteriously affect the power generation cycle and require extensive modifications from current design and operating experience. In sum, direct steam extraction as the heat source for flash evaporation desalinization is of limited usefulness.
To provide heat necessary for larger scale water-making capabilities, it has been proposed to utilize a "bob-tailed" turbine apparatus of a relatively large size, on the order of 1200 M.W. In such a scheme, the exhaust of the steam cycle is directly introduced as the heat source for the brine heater. The heat of condensation of the exhausted steam raises the temperature of the brine solution, while the condensate returns to the steam generator element of the power plant.
The main disadvantage of such an arrangement arises from the substitution of the brine heater for the standard condenser element. Such a substitution raises the back pressure -- the pressure immediately downstream of the last array of rotating blades -- so that there is little or no power generation from this blade array. It is apparent that such a condition would adversely affect the output and reliability of the electrical generating plant.
In order to obviate these difficulties due to the increased back pressure, it has been suggested that the rotating blades in the last array be shortened, or "bob-tailed", to a height less than the blade height for a normal last row blade of commensurate power capability. This tailoring of blade heights to meet system requirements and the resulting higher power density requires specially designed blades for each individual application. This, of course, precludes the use of proven and reliable standardized components. The probability of failure increases commensurately, and the efficiency and capability of the electrical plant is permanently impaired.
In addition, such plants may not be downed for repair without simultaneously halting desalinization procedures. Conversely, as long as the production of fresh water is required, the steam plant must be operated. Still further, by providing specially tailored blades, there may be generated severe control problems, especially in the overspeed control, due to the loss of rotational inertia.
It is apparent that there is required a steam power generation system having associated therewith an efficient heat cycle for large capability water desalinization able to deliver the maximum heat transfer yet still utilizing standardized proven components. It is also patent that a system and heat cycle utilizing heat extracted from a multiplicity of sources within the power plant to supply the heat load is a definite improvement over prior art systems. In addition, a heat cycle adaptable to divert steam to provide higher or lower water capability depending upon peak electricity demand, and to provide water desalinization during periods of turbine inactivity, is also advantageous over the present art.